Cystic fibrosis was diagnosed in two female infants, respectively nine months old (Case 1) and six months old (Case 2). Clinical presentation of these two infants showed frequent episodes of pneumonia, dehydration and poor weight gain, despite fair intake of food since birth. Hyponatremic, hypochloremic metabolic alkalosis had been found during their previous hospitalizations. In Case 1, stool fat was positive with negative trypsin test. Both cases had abnormal findings on chest X-ray films, but the pancreas showed no remarkable cystic changes from sonography. Plastic-bag method of sweat test showed Na/Cl: 155/185 nmol/L in Case 1, Na/Cl: 127/135 nmol/L in Case 2. A family history was suggested, since each one had an elder brother who had died in early infancy with similar clinical presentations. Both patients were put on special diet therapy as well as chest physical therapy. Case 1 died suddenly at 16 months of age. Autopsy revealed mucusplugged dilated ducts with atrophy of the exocrine portion of the pancreas. DNA analysis in Case 2 showed abnormal mutation point at 1898+5 G-->T on chromosome 7.